I assume this is Tokyo. Which airport, Haneda or Narita? Also, are arrival and departure airports the same?

There is no arrival lounge for that itinerary. But there are two hotels directly connected to terminal 3. Even with a 24 hour onsen in the vicinity of the terminal.

You can go in to a hotel. Have a bit of a walk around and dinner. Depending on where you go, you do need a bit early start to get back to the airport for a 10:20 departure, as you have to take morning rush hour in to account.

Sorry should have mentioned that, haneda.

Haneda is very close to central areas of the city. You could get a hotel in Shinagawa, which is a straight shot by train. The hotel options right around the airport are pretty good as well, and you would have dining options within walking distance. Check-in and security at Haneda is usually fast and I would aim to be there maybe 90 minutes before departure, which would mean leaving Shinagawa at 8:20ish (there shouldn't be too much traffic on the outbound Keikyu train at that time). The ANA lounge is OK but nothing to write home about.

First of all thanks to everyone for all your help. It's really been useful in my planning. I have a little bit of a curveball in that my flight changed and I now arrive in Narita on 9/26 and depart from haneda on 9/27.

Can anyone advise the best way to transfer between airports? Looks like there's a limousine bus that I can take that will take about an hour per Google maps

Skyaccess is the way to go!

Generally, I'd say the bus. Most of the day it is more frequent than the Skyaccess, about same time, and far more comfortable. But also a good deal more expensive.

What time to you arrive and then depart? Do you plan to go directly and stay at Haneda, or want to stay in town then go to Haneda next day? I realize that you have a bad leg, so don't want to do too much walking.

Pre-empting your response to Nishimark's questions -

If you're looking at an arrival at NRT in the morning or early afternoon and a mid-morning or later departure from HND, I would recommend overnighting in Tokyo itself rather than at the airport. OTOH, if you reach NRT late afternoon or evening and departing first thing from HND, and you want to minimize walking, you may prefer to jump on the limousine bus to HND and stay overnight at the airport.

I am planning to transfer at HND in mid December. It will be flying with AA and CA on two different itineraries so I guess the interline baggage check will not be possible. I will be going to going through the immigration, collect my baggage, re-check my baggage, and go through the security/immgration again. I will arrive HND at 5am and leave at 8:30am. I hear the the lines in HND are extremely long in HND these days, but I wonder if it is relaxed in the early morning.

I went through HND a couple of times last month. I had no problems with any long lines at Immigration or at a check-in desk. I don't think either one took more than 10 mins tops. I had built up an expectation of long lines and confusion and what I found was quite the opposite.

duckspeak,

Was there a couple of weeks ago on the early AA arrival. Immigration was just opening up, only a couple of booths open when we got there. More opened up within about 5 -10minutes. Did my Customs QR scan at the kiosk waiting for the bags to come down. Bags were the longest part of entry formalities, as usual. E-Gates weren't open yet but the Customs Inspector looked at my passport picture, said "Welcome to Japan. Have a Nice Day." and waved me through. Plane to lobby (trains didn't start for another hour) was 30 minutes, including the walk to Immigration.

You have more than enough time. All there is to do when you get there is to walk around the closed shopping area or head down to the 7-11 downstairs. Things were starting to open up in the check in area but since I was heading into town I didn't look very closely at what was open up there.

If you manage to check your bags through and have a connecting BP, the Transit checkpoint was open. Likely not that there was much happening on the departures level at that time in the morning.

Thank you for the information. I may choose to book JL flight with a few more bucks and hope AA through-check the bag with JL.

No problems with AA to JL bag transfers since they've got a JV for trans-Pac flights. You'll probably get your HND connection BP when you check in with AA.
You might want to check if either JL or AA have a one ticket option as well.

They do have one ticket options, but it is $1800 more expensive (round trip) than buying them separately.